Analysis and optimisation of combined cycles gas turbines working with partial recuperation

•Analysis of combined cycles (CC) with partial recuperative gas turbine (GT).•Configuration allows fuel saving avoiding the temperature decrease at the HRSG.•Comparison to conventional CC and CC with fully recuperative gas turbine.•CCs with partially-recuperative GT obtain the best thermodynamic and economic results. The objective of this paper is the analysis and the optimisation of several configurations of combined cycle gas turbines using a partially recuperative gas turbine and heat recovery steam generators (HRSG) of two and three pressure levels. The proposed configuration consists of the thermal recuperation of a fraction of the total exhaust gas mass flow, which preheats the air exiting from the compressor. The exhaust gas mass fraction that is not directed to the recuperator goes to the high temperature heat exchangers (superheaters and reheaters). As the temperature of the gas at the superheater inlet is maintained, the temperature of the produced steam is not decreased and the performance of the steam cycle is also maintained. In order to analyse and homogeneously compare the proposed configuration to the conventional and completely recuperative ones, three optimisations are carried out: (1) a thermodynamic optimisation, maximising the thermal efficiency; (2) a thermodynamic optimisation with the total heat exchange area constrained; and (3) a thermo-economic optimisation that minimises the generation cost. Results show the convenience of using recuperative gas turbines for the dual pressure configurations and, especially, the use of partial recuperation for both dual and triple pressure configurations. In almost all cases the optimal recuperative mass fraction is located at roughly 90%. In dual pressure level heat recovery steam generators, the use of a recuperative gas turbine is advisable both from the thermodynamic and economical points of view, but results are improved using high partial recuperation. In triple pressure level configurations, fully-recuperative gas turbines are not advisable but the performance and cost may be enhanced if the gas turbine is partially recuperative.